Niš, Serbia

Niš sits on the Nišava River in southern Serbia and ranks as the country's third-largest city, with a population of roughly 185,000. In 272 AD it was the birthplace of Constantine the Great, the Roman emperor who later legalized Christianity across the empire. The 18th-century Niš Fortress, raised by the Ottomans over an earlier Roman castrum, encloses 22 hectares of parks and an Ottoman hammam within its walls. Just 800 meters away stands Ćele Kula, the Skull Tower assembled in 1809 from the skulls of fallen Serbian rebels. The story behind those bones reshapes everything you think you knew about the city.